LR45 FLT CREW IS CLRED FOR STRAIGHT IN GPS RWY 24R APCH TO ENW. DSNDED TO MDA WHEN WITHIN 10 NM BECAUSE NO STEP DOWN FIX WAS PUBLISHED. LOW ALT ALERT IS GENERATED IN THE TWR.

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ON APCH INTO ENW; APCH CTL HANDED US TO TWR FOR THE VOR/GPS RWY 24R. WE CONTACTED TWR AND WITHIN 10 NM AS PER THE APCH; DSNDED BELOW 2500 FT DOWN TO THE FINAL MDA OF 1360 FT. AROUND 7 NM FROM THE VOR; TWR ADVISED US OF A TERRAIN ALERT! WE LOOKED PERPLEXED SINCE OUR ALT WITHIN 10 NM WAS AT 1360 FT FOR THE MDA WITHIN THE APCH PARAMETER AND WERE STARTING TO SEE THE WATER; THE COAST; AND THE ARPT. WE TOLD TWR ABOUT OUR VISUAL SITUATION AND TWR ADVISED US OF A TWR IN THE VICINITY THAT WE ACKNOWLEDGED AS HAVING IT IN SIGHT. WE BELIEVE THAT WE FLEW THE APCH AS PUBLISHED AND HAVING VISUAL; NO SAFETY PARAMETERS WERE COMPROMISED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT THEY WERE WBOUND; E OF ENW OVER LAKE MICHIGAN; WHEN MKE APCH CLRED THEM FOR A STRAIGHT IN GPS RWY 24R APCH. THE FLT CREW DISCUSSED THE LACK OF A PUBLISHED DSCNT POINT AND DECIDED THE PUBLISHED 10 MILE LIMIT FOR THE PROC TURN CONSTITUTED A VALID POINT AT WHICH A DSCNT BELOW THE PROC TURN ALT COULD BE INITIATED. RPTR STATED THE LOCAL CTLR SEEMED CONCERNED ABOUT THEIR ALT AND INQUIRED AT LEAST TWICE AS TO WHETHER THEY WERE HAVING A PROB. RPTR SUGGESTED THAT IF THERE WAS CONCERN REGARDING TERRAIN ON SUCH AN APCH IT SHOULD BE REQUIRED THAT APCH INCLUDE A 'MAINTAIN (AN APPROPRIATE) ALT UNTIL (A SPECIFIC) DME DISTANCE' RESTRICTION TO THE APCH CLRNC. RPTR MAINTAINS THAT THE FLT CREW'S ACTIONS WERE IN COMPLIANCE WITH BOTH THEIR CLRNC AND THE PARAMETERS OF THE APCH PLATE. RPTR COMMENTED THAT ANOTHER FLT CREW ADVISED THEY HAD EXPERIENCED THE SAME SITUATION ON AN EARLIER FLT.